Project Summary Bexarotene is a potent and selective retinoid X receptor (RXR) agonist (rexinoid) that is FDA-approved as an oral antineoplastic drug for cutaneous T-cell lymphoma (CTCL), but has also been explored in the treatment of other cancers. However, bexarotene only has ~45% response rate as a systemic therapy in later stages of CTCL, and while the response rate appears to improve at higher doses, there are dose-limiting toxicities associated with treatment. We propose to employ rational drug design to synthesize ~50 novel rexinoids (1-21 and 52-80 in the Research Plan) which display unique RXR binding properties that may render these analogs superior in biological potency and specificity, compared to bexarotene, as treatments for CTCL. Previously, we synthesized a panel of unique rexinoids with a variety of characteristics, including some analogs with superior efficacy and less severe side-effects relative to bexarotene. Utilizing our knowledge-base of previous rexinoids developed, tested, and validated by our group, we propose to synthesize a new suite of compounds which will be tested in a series of assays that contribute to a Biopotency Index Analysis (BIA) score. The BIA has been used to rank some of our existing compounds, and the ~50 new analogs we propose to develop are based on the structures of rexinoids with the highest BIA values. The BIA score is composed of several components that can be benchmarked to bexarotene or other target rexinoids (e.g.,NEt-TMN), including EC50 value, RXRE activation, modulation of anti-cancer gene expression, apoptotic effects, and anti-proliferative potency. The ~50 new analogs will be tested to assign BIA values. To determine RXR activation, we will assess each analog in a comprehensive panel of bioassays. We will first test the proposed rexinoid molecules in RXR yeast and mammalian two hybrid assays, as well as DNA-based (RXRE) assays to screen for RXR homodimer binding. Those analogs that display RXR binding/homodimerization will be further evaluated via testing of their modulation of anti-cancer genes (COX-2, DEPP, DEC2, IGFPD-6, etc.) and apoptotic genes (HDAC1, IkK, BIRC- 5, BO, etc.). The ~50 new rexinoids will also be assessed in apoptosis and proliferation assays in patient-derived CTCL cell lines (e.g., Hut78). The 3 rexinoids with the best BIA profiles will then be scaled up for testing in a novel mouse model of CTCL versus bexarotene and a vehicle control. Using interleukin-15 transgenic (IL-15tg) mice, we will determine the in vivo safety, tolerability and efficacy of selected rexinoids in CTCL. IL-15tg mice exhibit features of human CTCL, namely, cutaneous lesions characterized by erythematous plaques/patches, erythroderma, and pruritus compared to wild-type controls. Collectively, this approach will allow us to synthesize ~50 additional RXR agonists that may exhibit superior gene expression profiles that drive anti-cancer pathways in CTCL and then to validate this with in vitro and in vivo CTCL models. Our interdisciplinary and student- centered approach integrates medicinal chemistry, modeling, and a suite of biological assays to amplify our successful strategy of creating novel rexinoid pharmacotherapies suitable for clinical translation.